The present invention relates to a current-type converter apparatus, and in particular to a current-type converter apparatus suitable to output voltage control of a current-type converter using DC voltage as a power source and suitable to power conversion to the load in service interruption of the AC power source.
For an apparatus which controls a load such as a motor using a current-type converter including self-arc-suppressing devices such as transistors, there is a need of driving the motor even in service interruption of the Ac power source. As the prior art for satisfying such a need, a technique described in JP-A No. 61-102172, for example, is known. In this prior art, a DC power source such as a battery is used as a power source, and power supply means is disposed for controlling the output voltage of the DC power source by causing the power conversion operation of the above described current-type converter or a separately disposed apparatus, thus power being supplied to a load such as a motor.
In the above described prior art, only power running control means is considered, and braking means is not considered. For example, output voltage characteristics of output voltage obtained by the power supply means when the above described motor is changed to the power generation state by a load coupled to the motor has not been considered.
In general, a control device such as a semiconductor device included in a power supply means such as a current-type converter cannot be driven with a pulse width not larger than the minimum pulse width defined by the characteristics of that device. Therefore, the above described power supply means has a problem that the output voltage abruptly changes in a portion resulting in discontinuous characteristics. Further, there is a problem that the load cannot be controlled stably in the above described discontinuous output voltage region.
An object of the present invention is to provide a control unit of a current-type converter capable of having continuous output voltage characteristics even when a DC source is used as the power source.
Another object of the present invention is to provide a current-type converter unit capable of performing not only the power running control but also the electrical braking control of a motor even in service interruption of the current-type converter using an AC power source as the power source.